business statistics · bba lll sem. business statistics unit l . introduction: meaning and...

Biyani's Think Tank

Concept based material

Business Statistics BBA –lll Sem

Dr. Archana Dusad Assistant Professor

Deptt. of Commerce & Management Biyani Girls College, Jaipur

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Published by :

Think Tanks Biyani Group of Colleges Concept & Copyright :

Biyani Shikshan Samiti Sector-3, Vidhyadhar Nagar, Jaipur-302 023 (Rajasthan)

Ph : 0141-2338371, 2338591-95 Fax : 0141-2338007 E-mail : [email protected] Website :www.gurukpo.com; www.biyanicolleges.org First Edition : 2009 Second Edition: 2010 Price: Leaser Type Setted by : Biyani College Printing Department

While every effort is taken to avoid errors or omissions in this Publication, any

mistake or omission that may have crept in is not intentional. It may be taken note of

that neither the publisher nor the author will be responsible for any damage or loss of

any kind arising to anyone in any manner on account of such errors and omissions.

Statistical Methods 3

Preface

I am glad to present this book, especially designed to serve the needs of the

students. The book has been written keeping in mind the general weakness in understanding the fundamental concepts of the topics. The book is self-explanatory and adopts the “Teach Yourself” style. It is based on question-answer pattern. The language of book is quite easy and understandable based on scientific approach.

Any further improvement in the contents of the book by making corrections, omission and inclusion is keen to be achieved based on suggestions from the readers for which the author shall be obliged.

I acknowledge special thanks to Mr. Rajeev Biyani, Chairman & Dr. Sanjay Biyani, Director (Acad.) Biyani Group of Colleges, who are the backbones and main concept provider and also have been constant source of motivation throughout this Endeavour. They played an active role in coordinating the various stages of this Endeavour and spearheaded the publishing work.

I look forward to receiving valuable suggestions from professors of various educational institutions, other faculty members and students for improvement of the quality of the book. The reader may feel free to send in their comments and suggestions to the under mentioned address.

Author

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Syllabus BBA lll SEM.

BUSINESS STATISTICS

Unit l . Introduction: Meaning and Definition of Statistics, Scope of Statistics in Economics, Management, Science and Industry. Concept of Population and sample with illustration, Methods of Sampling SRSWR, SRSWOR, Stratified, Systematic. Data condensation and graphical methods. Raw Data, Attributes and variables, classification frequency distribution, cumulative frequency distribution Graphs- Histogram, Frequency Polygon Diagrams – Multiple bar, Pie, Subdivided bar. .

Unit ll Measuring of Central Tendency: Criteria for good measures of central tendency Arithmetic

Mean, Median, Mode for grouped and ungrouped data, combined mean. Unit lll Measures f Dispersion: Concept of Dispersion, Absolute and Relative Measures of

Dispersion, Range, Variance, Standard Deviation, Coefficient of variation, Quartile. Unit lV Correlation and Regression(For ungrouped data) : Concept of Correlation Positive and

Negative correlation, Karl Pearson‟s Coefficient of Correlation Meaning of Regression, Two regression equations, regression coefficients and properties.

Unit V Index Numbers : Meaning and Uses of Index Numbers, Simple and composite Index

Numbers, Aggregative and average of price Relatives – simple and weighted index numbers. Construction of index numbers fixed and chain base, Laspear, Paschee, Kelly, and Fisher index number :Construction of consumer price index case of limit index

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Content

S.No. Name of Topic

1. Meaning, Definition,and scope of Statistics

2. Functions, Importance and Distrust of Statistics

3. Statistical Investigation

4. Collection Of Data

5. Census and Sample Investigation

6. Editing of collected Data and Statistical Error

7. Classification and Tabulation of data

8. Diagrammatic and Graphic Presentation

9. Measure of central Tendency

10. Measure of Dispersion

11. Correlation

12. Linear Regression

13.

13. Index Number

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Chapter 1

Meaning, Definition and Scope of Statistics

Q.1 Define ‘Statistics’ and give characteristics of ‘Statistics’.

Ans.: „Statistics‟ means numerical presentation of facts. Its meaning is divided into

two forms - in plural form and in singular form. In plural form, „Statistics‟

means a collection of numerical facts or data example price statistics,

agricultural statistics, production statistics, etc. In singular form, the word

means the statistical methods with the help of which collection, analysis and

interpretation of data are accomplished.

Characteristics of Statistics -

a) Aggregate of facts/data

b) Numerically expressed

c) Affected by different factors

d) Collected or estimated

e) Reasonable standard of accuracy

f) Predetermined purpose

g) Comparable

h) Systematic collection.

Therefore, the process of collecting, classifying, presenting, analyzing and interpreting the numerical facts, comparable for some predetermined purpose are collectively known as “Statistics”.

Q.2 What is meant by ‘Data’?

Ans.: Data refers to any group of measurements that happen to interest us. These measurements provide information the decision maker uses. Data are the


foundation of any statistical investigation and the job of colleting data is the same for a statistician as collecting stone, mortar, cement, bricks etc. is for a builder.

Q.3 Discuss the Scope of Statistics.

Ans.: The scope of statistics is much extensive. It can be divided into two parts –

(i) Statistical Methods such as Collection, Classification, Tabulation, Presentation, Analysis, Interpretation and Forecasting.

(ii) Applied Statistics – It is further divided into three parts:

a) Descriptive Applied Statistics : Purpose of this analysis is to provide descriptive information.

b) Scientific Applied Statistics : Data are collected with the purpose of some scientific research and with the help of these data some particular theory or principle is propounded.

c) Business Applied Statistics : Under this branch statistical methods are used for the study, analysis and solution of various problems in the field of business.

Q. 4 State the limitation of statistics?

Ans. Scope of statistics are very wide. In any area where problems can be expressed in qualitative form, statistical methods can be used. But statistics have some limitations

1. Statistics can study only numerical or quantitative aspects of a problem.

2. Statistics deals with aggregates not with individuals.

3. Statistical results are true only on an average.

4. Statistical laws are not exact.

5. Statistics does not reveal the entire story.

6. Statistical relations do not necessarily bring out the cause and effect

relationship between phenomena.

7. Statistics is collected with a given purpose.

8. Statistics can be used only by experts.

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Chapter-2

Functions, Importance and Distrust of Statistics

Q.1 Give reasons for distrust in Statistics.

Ans.: By distrust of statistics we mean lack of confidence in statistical statements and statistical methods. It is often commented by people

“Statistics can prove anything.”

“There are three type of lies – lies, damned lies and statistics – wicked in the order of their naming.”

The main reasons for such views are -

a) Figures are convincing, and therefore people are easily led to believe them.

b) Ignorance of limitation of statistics.

c) Lack of test of accuracy.

d) Contradiction of data from actual circumstances.

e) Lack of specific ability to arrive at correct and appropriate results.

f) Can easily be manipulated.

Q.2 Discuss the functions and importance/utility of Statistics.

Ans.: Statistical methods are used not only in the social, economic and political fields but in every field of science and knowledge. Statistical analysis has become more significant in global relations and in the age of fast developing information technology.

According to Prof. Bowley, “The proper function of statistics is to enlarge individual experiences”.

Following are some of the important functions of Statistics :

a) To provide numerical facts.


b) To simplify complex facts.

c) To enlarge human knowledge and experience.

d) Helps in formulation of policies.

e) To provide comparison.

f) To establish mutual relations.

g) Helps in forecasting.

h) Test the accuracy of scientific theories.

i) To study extensively and intensively.

The use of statistics has become almost essential in order to clearly understand and solve a problem. Statistics proves to be much useful in unfamiliar fields of

application and complex situations such as :-

a) Planning

b) Administration

c) Economics

d) Trade & Commerce

e) Production management

f) Quality control

g) Helpful in inspection

h) Insurance business

i) Railways & transport Co

a) Banking Institutions

b) Speculation and Gambling

c) Underwriters and Investors

d) Politicians & social workers.

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Chapter 3

Statistical investigation

Q.1 What do you mean by statistical investigation?

Ans. In statistical investigation the search for the knowledge is done by means of collection of data through statistical methods. For any statistical enquiry, whether it is business, economics, political or social science, the basic problem is to collect facts and figures relating to a particular phenomenon expressed in terms of quantity or numbers.

Q.2 Write different stages of statistical inquiry serially?

Ans. The following are the various stages of a statistical inquiry:

1. Planning the Inquiry: A clear plan for investigation is made in the light of the

objects, scope, and nature, sources of information, units and method of collection

of data.

2. Collection of data: The next step for investigation is the collection of raw data.

Different types of questionnaires and schedules be prepared and dispatched to

related respondents for collection of data.

3. Editing of collected data: After collection of data, data is edited in the light of

standard of accuracy to be maintained.

4. Classification and tabulation of data: After editing, data is classified in different

classes and present the same in the forms of tables so that analysis is convenient.

5. Presentation of data: after classification and tabulation the data are presented in

the form of averages, diagrams or graphs etc.

6. Analysis of Data: The presented data are to be analyzed with the help of statistical

methods. The mathematical measures like averages, dispersion, correlation etc.

may be used for this purpose.

7. Interpretation and writing of the report: The last stage of investigation is the

suitable and proper interpretation and presentation of a report of investigation by


the investigator. Report will be concise and touch all the points regarding inquiry

to make it complete report.

Q.3 Discuss planning for a statistical investigation?

Ans. Quality of investigation results depends upon proper planning of investigation .The

following matters need careful consideration before the commencement of

investigation

1. Definition of the problem: The first step is to clearly state the problem indicating the

purpose for which inquiry is to be conducted, the type of information needed and the

use for which information obtained will be put.

2. Object of investigation: it is very essential for determining the nature of data to be

collected and technique to be employed it will help in eliminating the collection of

irrelevant data.

3. Scope of investigation: Scope of enquiry relates to the coverage with regards to the

type or information, subject matter and geographical area.

4. Time or Period of investigation : The investigation should be carried out within a

reasonable period of time, otherwise information collected may become outdated and

have no meaning at all.

5. Sources of information : After determination of object and period of investigation,

sources of information be decided. The sources may be Primary and Secondary.

6. Types of investigation: statistical investigation may be of the following types

Census or sample

Direct or indirect

Initial or repetitive confidential and public

Regular and Ad hoc

Official , semi official, or non official

Postal or personal

7. Statistical unit : it is a unit in terms of which the investigator counts or measures the

variables or attributes selected for enumeration.

8. Degree of accuracy desired: degree of accuracy required depends upon the object of

the enquiry.

9. Organization of investigation: Before the commencement of an enquiry the

preliminaries be decided.

10. Collection of data: At last the investigator starts the work of collection data. The

method of collection of data , the question to be included in a questionnaire, the size,

manner and necessary considerations for the inquiry are predetermined.

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Chapter 4

Collection of Data

Q.1 What do you mean by Collection of Data? Differentiate between Primary and

Secondary Data.

Ans.: Collection of data is the basic activity of statistical science. It means collection of facts and figures relating to particular phenomenon under the study of any problem whether it is in business economics, social or natural sciences.

Such material can be obtained directly from the individual units, called primary sources or from the material published earlier elsewhere known as the secondary sources.

Difference between Primary & Secondary Data

Primary Data Secondary Data

Basis nature Primary data are original and are collected for the first time.

Data which are collected earlier by someone else, and which are now in published or unpublished state.

Collecting Agency These data are collected by the investigator himself

Secondary data were collected earlier by some other person.

Post collection alterations

These data do not need alteration as they are according to the requirement of the investigation

These have to be analyzed and necessary changes have to be made to make them useful as per the requirements of investi-


gation.

Time & Money More time, energy and money has to be spent in collection of these data.

Comparatively less time and money is to be spent.

Q.2 What do you mean by Questionnaire? Give merits of a good Questionnaire.

Ans.: Questionnaire is a document containing questions related to the specific requirement

of a statistical investigation for collection of information which is filled by the

informants personally.

Requirements of a good questionnaire :-

Questions should be simple, clear and short.

Simple alternative or multiple choice questions.

Unambiguous and precise.

Questions should be in sequence.

Directly relative questions.

Test of accuracy.

No restricted questions affecting personal whims.

Assurance of secrecy to the informants.

Probability of a perfect answer.

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Chapter 5

Census and sample investigation

Q.1 What is Law of ‘Statistical Regularity’ and the Law of ’Inertia of Large Numbers’?

Ans.: Based on the mathematical theory of probability, Law of Statistical Regularity states

that if a sample is taken at random from a population, it is likely to possess the

characteristics as that of the population. A sample selected in this manner would be

representative of the population. If this condition is satisfied, it is possible for one to

depict fairly accurately the characteristics of the population by studying only a part

of it.

The Law of „Inertia of Large Numbers‟ is a corollary of the law of statistical

regularity. It states that, other things being equal, larger the size of sample, more

accurate the results are likely to be. This is because when large numbers are

considered, the variations in the component parts tend to balance each other and,

therefore, the variation in the aggregate is insignificant.

Q.2 What is Random Sampling?

OR

Define Random Sampling.

Ans.: Random Sampling is one in which selection of items is done in such a way that every item of the universe has an equal chance of being selected.

Random Sampling is based on probability and it is free from bias.

The different methods of Random Sampling are:-

a) Lottery method.

b) Rotating the drum.

c) By systematic arrangement.


d) Routed wheel method

e) By random numbers

Q.3 Define Stratified Random Sampling?

Ans.3. This sampling method is used when the population is comprised of natural subdivision of units. This method consists in classifying the population units into a certain number of groups called strata.

Then random samples are selected independently from each group.

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Chapter 6

Editing of Collected Data and Statistical Error

Q.1 What do you mean by Statistical Error? Give the difference between Mistake and

Error?

Ans.: The difference between the actual value of the figure and its approximated value is

called statistical error. For example if number of students of a college is 1,255 but in

round figures it is written as 1,300, then the difference is called „Statistical error‟. In

the words of Prof. Connor, “In statistical sense, „error‟ means the difference between

the approximate value and the true or ideal value, accurate determination of which is

not possible”.

Difference between Mistake and Error

Basis Mistake Error

a) Nature Committed

deliberately

Not deliberate

b) Source Due to use of wrong

method

Difference between

actual and

approximate value.

c) Estimation Difficult to estimate Can be estimated

d) Prevention Can be avoided by Cannot be avoided


carefulness easily.

e) State of

Occurrence

Can be committed at

any stage

Creeps in only at the

state of collecting,

analysis and

interpretation.

Q.2 Write a note on the Editing of Primary Data and Secondary Data for the purpose of Analysis and Interpretation.

Ans.: Before analysis and interpretation, it is necessary to edit the date to detect possible

errors and inaccuracies, so that accurate and impartial results may be obtained. Thus

editing means the process of checking for the errors and omissions and making

corrections, if necessary.

The task of editing is a highly specialized one and requires high level of skill and

carefulness to attain the proper degree of accuracy.

Editing of Primary Data : While editing primary data, the following points should be

considered :-

Editing for consistency

Editing for completeness

Editing for accuracy

Editing for uniformity or homogeneity

Editing of Secondary Data : Since secondary data have already been obtained, it is

highly desirable that a proper scrutiny of such data is made before they are used by

the investigator. Bowley rightly points out that “secondary data should not be

accepted at their face value”.

Hence before using secondary data, the investigators should consider the following

aspects :-

Whether the Data are Suitable for the Purpose of Investigation in View :

Quite often secondary data do not satisfy immediate needs because they have

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been compiled for other purpose. The variation can be in units of

measurement, variation in the date/period to which data is related etc.

Whether the Data is Adequate for the Investigation : Adequacy of data is to

be judged in the light of the requirements of the survey and the geographical

area covered by the available data. For example if our object is to study ;the

wage rates of the workers in sugar industry in India and the available data

cover only the state of Rajasthan, it would not serve the purpose.

Whether the Data are Reliable : The following points should be checked to

find out the reliability of secondary data -

(i) The collecting agency was unbiased.

(ii) The enumerators are properly trained.

(iii) A proper check on the accuracy of the field work.

(iv) Was the editing, tabulating and analysis carefully and conscientiously

done.

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Chapter 7

Classification and Tabulation of Data

Q.1 What is the meaning of Classification? Give objectives of Classification and

essentials of an ideal classification.

Ans.: Classification is the process of arranging data into various groups, classes and sub-classes according to some common characteristics of separating them into different but related parts.

Main objectives of Classification :-

(i) To make the data easy and precise

(ii) To facilitate comparison

(iii) Classified facts expose the cause-effect relationship.

(iv) To arrange the data in proper and systematic way

(v) The data can be presented in a proper tabular form only.

Essentials of an Ideal Classification :-

(i) Classification should be so exhaustive and complete that every individual unit is included in one or the other class.

(ii) Classification should be suitable according to the objectives of investigation.

(iii) There should be stability in the basis of classification so that comparison can be made.

(iv) The facts should be arranged in proper and systematic way.

(v) Data should be classified according to homogeneity.

(vi) It should be arithmetically accurate.

Q.2 What is Manifold Classification?

Ans.: When the data are classified into more than two classes according to more than one attribute, it is called manifold classification.

Q.3 What are Class Limits?

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Ans.: The two values which determine a class are known as class limits. First or the smaller one is known as lower limit (L1) and the greater one is known as upper limit (L2)

Q.4 How many types of Series are there on the basis of Quantitative Classification? Give the difference between Exclusive and Inclusive Series.

Ans.: There are three types of frequency distributions -

(i) Individual Series : In individual series, the frequency of each item or value is only one for example ;marks scored by 10 students of a class are written individually.

(ii) Discrete Series : A discrete series is that in which the individual values are different from each other by a different amount.

For example: Daily wages 5 10 15 20

No. of workers 6 9 8 5

(iii) Continuous Series : When the number of items are placed within the limits of the class, the series obtained by classification of such data is known as continuous series.

For example Marks obtained 0-10 10-20 20-30 30-40

No.of students 10 18 22 25

Difference between Exclusive and Inclusive Series

Exclusive Series Inclusive Series

Limits Upper limit of one class is equal to the lower limit of next class.

The two limits are not equal.

Inclusion The value equal to the upper limit is included in the next class.

Both upper & lower limits are included in the same class.

Conversion It does not require any conversion.

Inclusive series is converted into exclusive series for calculation purpose.


Suitability It is suitable in all situations.

It is suitable only when the values are in integers.

Q.5 What is Bivariate Frequency Distribution?

Ans.: A frequency distribution obtained by the simultaneous classification of data according to two characteristics is known as a bivariate frequency distribution.

Q.6 Give Sturges Formula for determining Magnitude of Classes?

Ans.: According to Prof. A. H. Sturges, class interval can be found using the following formula.

I = L - S

1 + 3.322 log N

Where -

I = class interval N = No. of observations

L = Largest value S = Smallest value

Q.7 Define Tabulation. State the objectives of Tabulation and kinds of Tables.

Ans.: According to Blair, “Tabulation in its broad sense is an orderly arrangement of data in columns and rows.”

Tabulation is a process of presenting the collected and classified data in proper order and systematic way in columns and rows so that it can be easily compared and its characteristics can be elucidated.

Objects of Tabulation :

Orderly and systematic presentation of data.

Making data precise and stable.

To facilitate comparison.

To make the problem clear and self evident.

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To facilitate analysis & interpretation of data.

Kinds of Table : The different kinds of tables are showned in the following chart -

Table

On the basis of Purpose

On the basis of Origin

On the basis of Construction

General Purpose

Table

Specific Purpose

Table

Original /

Primary Table

Derived Secondary

Table

Simple Table

Complex Table

Double / Two-way Table

Triple / Three – way Table

Multiple / Higher Order Table

Q.8 What are the main parts of a good Table?

Ans.: The number of parts depends mostly on the nature of the data. However, a table should have the following parts.

(i) Table No. : Each table should be numbered so that the table may be referred with that number.

(ii) Title : Every table must be given a suitable title which should be short, clear and complete.

(iii) Captions : Caption refers to the column heading which explains what the column represents.

(iv) Stubs : Stubs are the designations of the rows or row headings.

(v) Body : It is the heart of the table. The body of the table contains the numerical information.


(vi) Ruling and Spacing : Ruling and leaving the space depends on the needs of the topic and makes the table attractive and beautiful.

(vii) Footnotes : In order to explain the figures shown in the table, explanatory notes may be given at the end of the table.

(viii) Source : At the end of the table, the source or origin of given data is mentioned.

□ □ □

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Chapter 8

Diagrammatic and Graphic Presentation

Q.1 what is Diagrammatic Representation? State the importance of Diagrams.

Ans.: Depicting of statistical data in the form of attractive shapes such as bars, circles, and

rectangles is called diagrammatic presentation.

A diagram is a visual form of presentation of statistical data, highlighting their basic

facts and relationship. There are geometrical figures like lines, bars, squares,

rectangles, circles, curves, etc. Diagrams are used with great effectiveness in the

presentation of all types of data.

When properly constructed, they readily show information that might otherwise be

lost amid the details of numerical tabulation.

Importance of Diagrams :

A properly constructed diagram appeals to the eye as well as the mind since it is

practical, clear and easily understandable even by those who are unacquainted with

the methods of presentation. Utility or importance of diagrams will become clearer

from the following points -

(i) Attractive and Effective Means of Presentation: Beautiful lines; full of various

colours and signs attract human sight, and do not strain the mind of the

observer. A common man who does not wish to indulge in figures, get

message from a well prepared diagram.

(ii) Make Data Simple and Understandable : The mass of complex data, when

prepared through diagram, can be understood easily. According to Shri

Morane, “Diagrams help us to understand the complete meaning of a complex

numerical situation at one sight only”.


(iii) Facilitate Comparison : Diagrams make comparison possible between two

sets of data of different periods, regions or other facts by putting side by side

through diagrammatic presentation.

(iv) Save Time and Energy : The data which will take hours to understand,

becomes clear by just having a look at total facts represented through

diagrams.

(v) Universal Utility : Because of its merits, the diagrams are used for

presentation of statistical data in different areas. It is widely used technique in

economic, business, administration, social and other areas.

(vi) Helpful in Information Communication : A diagram depicts more

information than the data shown in a table. Information concerning data to

general public becomes more easy through diagrams and gets into the mind of

a person with ordinary knowledge.

Q.2 Explain in brief the various types of Diagrams?

Ans.: The different types of diagrams can be divided into following heads -

(1) One dimensional diagrams

(2) Two dimensional diagrams

(3) Three dimensional diagrams

(4) Pictograms

(5) Cartograms

(1) One Dimensional Diagrams or Bar Diagrams :

Bar diagrams are the most common types of diagram. A bar is a thick line

whose width is shown merely for attention. They are called one dimensional

because it is only the length of the bar that matters and not the width.

Kinds of Bar Diagrams :

(i) Line Diagrams : When the number of items is large, but the proportion

between the maximum and minimum is low, lines may be drawn to

economise space. Only individual or time series are represented by

these diagrams

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(ii) Simple Bar Diagrams : A simple bar diagram is used to represent only

one variable. For example the figures of sales, production etc. of

various years may be shown by means of simple bar diagram. The bars

are of equal width only the length varies.

These diagrams are appropriate in case of individual series, discrete

series and time series.

(iii) Multiple Bar Diagrams : In a multiple bar diagram, two or more sets of

interrelated data are represented. Different shades, colors or dots are

used to distinguish between the bars.

These are used to compare two or more related variables based on time

and place.

(iv) Sub-divided Bar Diagrams : If a bar is divided into more than one

parts, it will be called sub-divided bar diagram. Each component

occupies a part of the bar proportional to its share in the total. For

example total expenditure incurred by a family on various items such

as food, clothing, education, house rent etc can be represented by

means of sub-divided bar diagram.

(v) Percentage Sub-Divided Bar Diagrams : Percentage sub-divided bars

are particularly useful to measure relative changes of data. When

such diagrams are prepared, the length of the bar is kept equal to 100

and segments are cut in these bars to represent the components of an

aggregate.

(vi) Profit – Loss Diagrams : If relative change of cost & sales or profit or

loss are to be represented with the help of bars, then profit – loss

diagram are constructed. These diagrams are similar to percentage sub-

divided bars and are prepared in the same way.

(vii) Duo-Directional Bar Diagrams : In duo-directional bar diagram

comparative study of two major parts of data is represented in a single

bar. Such duo directional diagrams are represented on both sides of the

horizontal axis, i.e. above and below the base line.

(viii) Paired Bars : If two different informations which are in different units

are to be presented then paired bar diagram are used. These bars are


not vertical but horizontal and the first scale is in the first half and

second scale is in the second half.

(ix) Deviation Bar Diagram : Deviation bars are popularly used for

representing net quantities i.e. net profit, net loss, net exports or net

imports etc. Such bars can have both positive or negative values.

Positive values are shown above the base line and negative values

below it.

(x) Progress Chart or Gant Chart : These charts are mainly used in

factories for comparing the actual production with targeted production.

By looking at it, it can be known how much production has been

achieved and how much they are lacking behind the capacity.

(xi) Pyramid Bar Diagram : These diagrams are constructed to show

population distribution. The distribution of population according to

sex, age, education etc are represented by this diagram. In this

diagram, the base line is in the middle and its shape is like a pyramid.

(xii) Sliding Bar Diagrams : These bars are like deo-directional bars but

instead of absolute figures percentages of two variables are shown.

One of them is shown on the right side of the base and the other on its

left.

(2) Two Dimensional Diagrams :

In two dimensional diagrams, the height as well as the width of the bars will

be considered. The area of the bars represents the magnitude of data. Such

diagrams are also known as area diagrams or surface diagrams.

The important types are –

(i) Rectangle diagram

(ii) Square diagram

(iii) Circle or Pie diagram

(i) Rectangle Diagram: Rectangles are often used to represent the relative

magnitude of two or more values. The area of rectangles is kept in

proportion to the values.

They are placed side by side like bars and uniform space is left between

different rectangles.

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The rectangles may be of different types -

a) Simple Rectangles

b) Sub-divided Rectangles

c) Percentage sub-divided Rectangles

(ii) Square Diagrams : When there is a large difference between the

extreme values (example the smallest value is 4 and the biggest value is

800) is such a case square diagram is more appropriate.

First of all square roots of the given values are calculated and the sides

are taken in the proportion of square roots. The squares are drawn on

the common base line, serially either in increasing or decreasing heights

to have beautiful and attractive appearance.

For calculating the scale, the area is calculated by squaring its side, on

the basis of that value of 1 sq.cm. is calculated.

(iii) Circle or Pie Diagram : These diagrams are more attractive, therefore,

pie diagrams are preferred to square diagrams. These diagrams are

used to represent data of population, foreign trade, production etc.

The square roots of the given values are calculated and then it is

divided by some common factor so as to attain the radii for the circles.

The area of the circle is calculated by the formula - (r2) . The sides for

squares are taken as the radii for different circles.

A circle can also be sub-divided on the basis of angles to be calculated

for each component. There is 360 degree at the centre of the circle and

proportionate sectors are cut taking the whole data equal to 360

degrees. Such a circle is known as sub-divided circle or Angular

diagram.

(3) Three Dimensional Diagrams :

In three-dimensional diagrams length, width and height (depth) are taken into

consideration. If the difference between the minimum and maximum value is

so wide as it is difficult to represent them by square or circle diagram, then

three dimensional diagram is used. For this cubic roots of the given numbers

is calculated. Three dimensional diagrams include cubes, blocks, spheres and

cylinders etc.


(i) Pictorgrams : Pictograms are used by government and non-government

organizations for the purpose of advertisement and publicity through

appropriate pictures. It is a popular technique particularly when

statistical facts are to be presented for a layman having no background

of mathematics or statistics.

For representing data relating to social, business and economic

phenomena for general masses in fairs and exhibitions, this method is

used.

(ii) Cartograms : Cartograms or statistical maps are also used to represent

data. Cartograms are simple and elementary form of visual

presentation and are very easy to understand.

While highlighting the regional or geographical comparisons,

mapographs or cartograms are generally used.

Q.3 What is Graphic Presentation?

Ans.: According to M.M. Blair – “ The simplest to understand, the easiest to make, the

most variable and the most widely used type of chart is graph.”.

Graphic presentation is a visual form of presenting statistical data. Graph acts as a

tool of analysis and makes complex data simple and intelligible.

Graphs are more appropriate in the following cases -

a) If tendency instead of real measurement is important.

b) When comparative study of many data series is required on one graph.

c) If estimation and interpolation are to be presented by graph.

d) If frequency distribution is presented by two or more curves.

Q.4 What is False Base Line?

Ans.: While making the graph the vertical scale (y-axis) must start from zero origin. But in

some cases adjustment of scale is not possible on (y-axis) starting with zero since the

values are big. If the vertical scale begins with zero, the curve will be concentrated

mostly on the top of the graph paper.

30

In such cases that portion of the scale from zero to the minimum value of items to be

depicted is omitted. This fact is indicated in the graph paper itself either by drawing a

double saw tooth lines in the empty space or by a cut in y-axis. This is known as

using false base line. It is drawn in this way to show that Y axis is lost in between.

Q.5 What is Historigram? Give the difference between Absolute Historigram and

Index Historigram.

Ans. The curve drawn on graph paper by presenting variables of time series is called

„Historigram‟, because it reveals the past history of data. A time series is an

arrangement of statistical data in a chronological order with reference to occurrence

of time. Time period may be a year, quarter, month, week, days, hours etc. Such

graphs may be drawn on natural scale or ratio scale.

When actual values of a variable are plotted on a graph paper, it is called absolute

historigram. Absolute historigram can be of (i) one variable (ii) two or more

variables.

Index historigrams are obtained by plotting index numbers of actual values on a

graph paper. If index numbers are not given, the same may be calculated of the

original values. It shows relative changes.

Q.6 What are the various types of graphs of frequency distribution?

Ans.: Frequency distribution can also be presented by means of graphs. Such graphs

facilitate comparative study of two or more frequency distributions as regards their

shape and pattern. The most commonly used graphs are as follows -

(i) Line frequency diagram

(ii) Histogram

(iii) Frequency Polygon

(iv) Frequency curves

(v) cumulative frequency curves or Ogine curves

Line Frequency Diagram : This diagram is mostly used to depict discrete series on a

graph. The values are shown on the X-axis and the frequencies on the Y axis. The

lines are drawn vertically on X-axis against the relevant values taking the height

equal to respective frequencies.


Histogram : It is generally used for presenting continuous series. Class intervals are

shown on X-axis and the frequencies on Y-axis. The data are plotted as a series of

rectangles one over the other. The height of rectangle represents the frequency of that

group. Each rectangle is joined with the other so as to give a continuous picture.

Histogram is a graphic method of locating mode in continuous series. The rectangle

of the highest frequency is treated as the rectangle in which mode lies. The top

corner of this rectangle and the adjacent rectangles on both sides are joined

diagonally . The point where two lines interact each other a perpendicular line is

drawn on OX-axis. The point where the perpendicular line meets OX-axis is the

value of mode.

Frequency Polygon : Frequency polygon is a graphical presentation of both discrete

and continuous series.

For a discrete frequency distribution, frequency polygon is obtained by plotting

frequencies on Y-axis against the corresponding size of the variables on X-axis and

then joining all the points ;by a straight line.

In continuous series the mid-points of the top of each rectangle of histogram is joined

by a straight line. To make the area of the frequency polygon equal to histogram, the

line so drawn is stretched to meet the base line (X-axis) on both sides.

Frequency Curve : The curve derived by making smooth frequency polygon is called

frequency curve. It is constructed by making smooth the lines of frequency polygon.

This curve is drawn with a free hand so that its angularity disappears and the area of

frequency curve remains equal to that of frequency polygon.

Cumulative Frequency Curve or Ogine Curve : This curve is a graphic presentation

of the cumulative frequency distribution of continuous series. It can be of two types -

(a) Less than Ogive and

(b) More than Ogive.

Less than Ogive : This curve is obtained by plotting less than cumulative frequencies

against the upper class limits of the respective classes. The points so obtained are

joined by a straight line. It is an increasing curve sloping upward from left to right.

More than Ogive : It is obtained by plotting „more than‟ cumulative frequencies

against the lower class limits of the respective classes. The points so obtained are

joined by a straight line to give „more than ogive‟. It is a decreasing curve which

slopes downwards from left to right.

32

Chapter 9

Measures of Central Tendency

Q.1 What do you mean by Measures of Central Tendency? Define Arithmetic Mean,

Mediam and Mode.

Ans. : The central tendency of a variable means a typical value around which other values tend to concentrate; hence this value representing the central tendency of the series is called measures of central tendency or average.

According to Clark, “Average is an attempt to find one single figure to describe whole of figures.”

Arithmetic Mean (X) : The most popular and widely used measure of representing the entire data by one value is known as arithmetic mean. Its value is obtained by adding together all the items and by dividing this total by the number of items.

Arithmetic mean may be of two types :

Simple Arithmetic mean

Weighted arithmetic mean

Calculation of Arithmetic Mean :

Individual Series Discrete & continuous series

Direct Method : X = ∑X N Where – X Values N No. of Items

Direct Method : X = ∑f X N Where – fX Values X frequencies N Total of frequencies

Shortcut Method : X = A + ∑dx N Where – A Assumed Mean

Shortcut Method : X = A + ∑f dx N


dx X - A Step-Deviation Method : Not applicable

Step-Deviation Method : X = A + ∑f dx ‟ X i N Where – dx ‟ X – A i i Class interval

Median (M) : Median is that value of the variable which divides the group into two equal parts, one part comprising all values greater than, and the other all values less than the median

Calculation of Median :

a) Individual Series :

Arrange the variables in ascending or descending order.

M = size of N+1 th item

2

Where N –> No. of items

b) Discrete Series :


Calculate cumulative frequencies.

Apply formula M = N+1 th item; N = Total of frequency.

2

The value (X) corresponding to this in the cumulative frequency will be the median.

c) Continuous Series :


Calculate cumulative frequencies.

Determine median class by using (N/2).

Apply formula –

M = l1 + i (m – c)

f

34

l1 lower limit of median group

i class interval

m N/2

c cumulative frequency preceding the median group.

f frequency of median group

Mode (Z) : Mode is the value that appears most frequently in a series i.e. it is the value of the item around which frequencies are most densely concentrated.

Calculation of Mode :

a) Individual Series :

(i) By inspection – value repeated most.

(ii) By converting individual series into discrete series.

(iii) By empirical relationship between the averages -

Z = 3M – 2X

b) Discrete Series :

(i) By inspection – value having highest frequency.

(ii) By grouping.

(iii) By empirical relationship.

c) Continuous Series :

(i) First calculate model class by inspection or by grouping.

(ii) Then apply the following formula -

l1 + ∆1

∆1 + ∆2

where l1 lower limit of modal class

∆1 f1 – f0

∆2 f1 – f2

f1 frequency of modal class

f0 frequency of preceding class.


f2 frequency of succeeding class

i class interval

Q.2 What are the essentials of an Ideal Average.

Ans.: (i) Should be easy to understand.

(ii) Clearly and rigidly defined.

(iii) Based on all the observations.

(iv) Simple to compute.

(v) Least affected by fluctuations.

(vi) Capable of further Algebraic treatment.

(vii) Sampling stability.

Q.3 What is Geometric Man? Give Algebraic Characteristics of Geometric Mean and state when Geometric Mean is useful.

Ans.: Geometric mean is the nth root of the product of N items or values.

Calculation of Geometric Mean (G) :

Individual Series Discrete & Continuous Series

G = Antilog ∑ log X

N

G = Antilog ∑f log X

N

Algebraic Characteristics of Geometric Mean :

(ii) The product of the items remains unchanged if each item is replaced by geometric mean.

(iii) Geometric mean cannot be found if the value of some item in the series is negative or zero.

(iv) The product of corresponding ratios on either side of the geometric mean is always equal.

(v) Not affected by changing the sequence of items.

Geometric mean is appropriate or useful :-

- When ratios or percentages are to be found.

36

- In determining rates of increase or decrease.

- When the different values are at vast difference.

Q.4 What is Harmonic Mean? In which circumstances Harmonic Mean is used.

Ans.: Harmonic mean of a series is the reciprocal of the arithmetic mean of the reciprocal of the values of its items.

Calculation of Harmonic Mean (H.M.) :


H.M. = Reciprocal ∑ Reci.X

N

H.M. = Reciprocal ∑ (Reci.X .f)

N

Harmonic Mean is used in the following cases :-

- For determining average speed or velocity.

- To find out average price.

- If the item given in the question which is variable is to be kept as constant in the answer, or vice versa, then harmonic mean will be calculated.

Q.5 What is Partition Value. Give formula for calculating different Partition Values?

Ans.: Values of the items that divide the series into many parts are known as partition values. A variable may be divided into four, five, eight, ten and hundred equal parts known as Quartiles, Quintiles, Octiles, Deciles and Percentiles. The aforesaid partition values gives an idea of the formation of the series which are used in the calculation of dispersion and skewness.


Formula used for Calculating Partition Values :

Measures Individual & Discrete Series

Continuous Series

Quartiles :

Q1 Size of N + 1 th item

4

q1 = (N/4) th item & Q1 = l1 + i (q1 – c)

f

Q3 Size of 3 N + 1 th item

4

q3 = 3 (N/4) th item & Q3 = l1 + i (q3 – c)

f

Quintiles :

Qn4

Size of 4 N + 1 th item

5

qn4 = 4 (N/5) th item & Q3 = l1 + i (qn4 – c)

f

Octiles :

O2


8

o2 = 2 (N/8) th item & O2 = l1 + i (o2 – c)

f

Deciles :

D7


10

d3 = 7 (N/10) th item & D3 = l1 + i (d7 – c)

f

Percentiles:

P75


100

775 = 75(N/100)th item & P75 = l1 + i (p75 – c)

f

Q.6 How are Arithmetic Mean, Geometric Mean and Harmonic Mean related to each other? Why is Arithmetic Mean greater than the Geometric Mean and Geometric Mean is greater than the Harmonic Mean.

Ans.: Relation between arithmetic mean, geometric mean and harmonic mean can be given by -

(i) X > g > h and (ii) g2 = X.h.

While calculating arithmetic mean, the bigger values are given more weightage than the small values, whereas in harmonic mean the smaller values are given much more weightage than to the larger values. Therefore, arithmetic mean is greater than geometric mean and geometric mean is greater than harmonic mean.

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38

Chapter 10

Measures of Dispersion

Q.1 What do you mean by Dispersion. Give the meaning of Absolute Measure and

Relative Measure with example.

Ans. : Dispersion is a measure of the extent to which the individual item vary from a central value Dispersion is used in two senses, (i) difference between the extreme items of the series and (ii) average of deviation of items from the mean.

Absolute Measure : The figure showing the limit or magnitude of dispersion is known as absolute measure and it is shown in the same unit as ;those of the original data, example measures of dispersion in the age of students, their height, weight etc.

Relative Measure : For comparative study the concerning absolute measure is divided by the corresponding mean or some other characteristic value to obtain a ratio or percentage, which is known as the relative measure.

Q.2 Explain the various methods for measuring Dispersion. Also give their merits and demerits?

Ans.: Following are the important methods of studying dispersion - (1) Numerical Methods:

a) Methods of limits b) Methods of average deviation:

i) Range i) Quartile Deviation ii) Inter-quartile range ii) Mean Deviation iii) Percentile Range iii) Standard Deviation (2) Graphic Method - Lorenz Curve:

i) Range: The difference between the value of the smallest item and the value of the largest item of the series is called range.

Range = Largest item – Smallest item Co-efficient of Range = L - S L + S Merits of Range :


- Simple and easy to be computed. - It takes minimum time to calculate. - Not necessary to know all the values, only smallest and largest

value is required. - Helpful in quality control of products. Demerits of Range : - Not based on all the items. - Subject to fluctuation/uncertain measure. - Cannot be computed in case of open-end distributions. - As it is not based on all the values it is not considered as a good

or appropriate measure. ii) Inter-Quartile Range : Inter-quartile range represents the difference

between the third-quartile and the first quartile. It is also known as the range of middle 50% values. Inter-quartile range = Q3 – Q1 Merits:

- It is easy to calculate. - Can be measured in open end distributions.

- It is least affected by the uncertainty of the extreme values.

Demerits:

- It does not represent all the values.

- It is an uncertain measure.

- It is very much affected by sampling fluctuations.

iii) Percentile Range: It is the difference between the values of the 90th and 10 th percentile. It is based on the middle 80% items of the series.

Percentile Range = P90 – P10

Merits and Demerits : Its use is limited. Percentile range has almost the same merits and demerits as those of inter-quartile range.

iv) Quartile Deviation / Semi – Interquartile Range :

Quartile Deviation gives the average amount by which the two quartiles differ from the median. Quartile deviation is an absolute measure of dispersion.

It is calculated by using the formula -

Q.D. = Q3 – Q1 , coefficient of Q.D. = Q3 – Q1

40

2 Q3 + Q1

Merits:

- It is easy to calculate and understand.

- It has a special utility in measuring variation in open end distributions.

- QD is not affected by the presence of extreme values. Demerits :

- It is very much affected by sampling fluctuations. - It does not give an idea of the formulation of the series. - It is not capable of further algebraic treatment.

v) Mean Deviation () : Mean Deviation is also known as average deviation or first measure of dispersion. It is the average difference between the items in a distribution and the median mean or mode of that series. Computation of Mean Deviation:

Individual Series Discrete & continuous

series

a) Deviation from Mean : X = ∑│dx│ , │dx│ = │X - X│ N Coefficient of X = X X

a) Deviation from Mean : X = ∑f│dx│ N

b) Mean Deviation from Median : M = ∑│dM│ ,│dM│ = │X - M│ N Coefficient of M = M M

b) Mean Deviation from Median : M = ∑f│dM│ N


c) Mean Deviation from Mode : Z = ∑│dZ│ ,│dZ│ = │X - Z│ N Coefficient of Z = Z M

b) Mean Deviation from Mode : M = ∑f│dZ│ N

Merits :

- It is simple to understand and easy to compute.

- Based on each and every item of the data.

- Least affected by the extreme values.

- It can be computed from any average, mean, median or mode.

Demerits :

- Signs are ignored therefore mathematically it is incorrect and not a significant measure.

- Cannot be compared if mean deviations of different series are based on different averages.

- Does not give accurate results.

vi) Standard Deviation (σ) :

Standard Deviation was introduced by Karl Pearson in 1823. It is the most important and widely used measure of studying dispersion, as it is free from those defects from which the earlier methods suffer and satisfies most of the properties of a good measure of dispersion.

Standard Deviation is the square root of the average of the square deviations from the arithmetic mean of a distribution.

Co-efficient of Standard Deviation :

Standard deviation is an absolute measure. When comparison of variability in two or more series is required, relative measure of standard deviation is computed which is called coefficient of standard deviation.

42


Direct Method :

σ = ∑d2

N

Where –

d2 (X – X) 2

N No. of Items

Direct Method :

σ = ∑fd2

N

Shortcut Method :

σ = ∑dx2 ∑dx 2

N N

Where –

dx2 (X – A) 2

A Assumed Mean

Shortcut Method :

σ = ∑fdx2 ∑fdx 2

N N

Computation of Standard Deviation: Coefficient of S.D. = σ / X Variance = σ2 Coefficient of variation: Coefficient of variation is used for the comparative study of stability or homogeneity in more than two or more series. C.V = σ X 100

X Merits: - Based on all the items. - Well-defined and definite measure of dispersion.

- Least affected by sample fluctuations.

- Suitable for algebraic treatment.

Demerits :

- Standard Deviation is comparatively difficult to calculate.

- Much importance is given to the extreme values.

vii) Graphical Method - Lorenz Curve :


This curve was devised by Dr. Max O‟Lorenz. He used this technique to show inequality of wealth and income of a group of people. It is simple, attractive and effective measure of dispersion, yet it is not scientific since it does not provide a figure to measure dispersion.

Merits :

- Easy to understand from the graph.

- Comparison can be done in two or more series.

- Attractive & effective.

- Concentration or density of frequency can be known from the curve.

Demerits :

- It is not a numerical measure; therefore it is not definite as a mathematical measure.

- Drawing of curve requires more time and labour.

Q.3 What is the best method of measuring Dispersion. Write the formula for calculating combined S.D.

Ans.: Standard Deviation is the best method of measuring dispersion as deviations taken from mean and algebraic signs are not ignored and it is algebraically correct.

Formula for calculating combined Standard Deviation :

σ12 = N1 (σ12 + D12) + N2 (σ22 + D22) + - - - - - - - - - -

N1 + N2

Where –

N1 & N2 No. of items of two series

σ1 & σ 2 S.D. of the two series

D1 X1 – X12

D2 X2 – X12

X12 Combined arithmetic mean

□ □ □

44

Chapter 11

Correlation

Q.1 What is Correlation. State the different types and degrees of Correlation.

Ans.: If two series vary in such a way, that fluctuations in one are accompanied by the fluctuations in the other, these variables are said to be correlated. Like rise in price of a commodity, reduces its demand and vica-versa.

Some relationship exists between age of husband and wife, rainfall and production. Two variables are said to be correlated if the change in one variable results in a corresponding change in the other variable.

According to A. M. Tuttle, “Analysis of co-variation of two or more variables is usually called correlation”.

Types of Correlation : Correlation can be of following types -

(i) Positive and Negative Correlation : If changes in two connected series is in the same direction, i.e. increase in one variable is associated with increase in other variable, the correlation is said to be positive. For example increase in father‟s age, increase in son‟s age.

If the two related series change in opposite direction i.e. increase in one variable is associated with the corresponding decrease in other variable, the correlation is said to be negative.

(ii) Linear an Non-Linear : If the amount of change in one variable tends to bear constant ratio of change in the other variable, the correlation is said to be linear. We get a straight line if the variables of these series are marked on graph paper.

Correlation would be called non-linear or curvilinear if the amount of change in one variable does not bear a constant ratio to the amount of change in the other variable. For example if we double the amount of rainfall the production would not necessarily be doubled.


(iii) Simple, Partial and Multiple Correlation : When only two variables are

studied, it is called simple correlation.

If the common effect of two or more independent variables on one dependent

data series is studied, it is called multiple correlations. For example if the

study of rain, soil, temperature on potato production per acre is studied then it

is multiple correlation.

On the other hand, in partial correlation we recognize more than two

variables, but consider only two variables to be influencing each other, the

effect of other influencing variables being kept constant.

Degree of Correlation : The interpretation of co-efficient of correlation is based on

the degree of correlation. The coefficient may be in the following degrees -

(i) Perfect Correlation :

a) Perfect positive correlation (r) = +1

b) Perfect negative correlation (r) = -1

(ii) Absence of Correlation or No Correlation :

r = o

(iii) Limited Degree of Correlation :

(a) High degree positive or negative ±0.75 to 1.00

(b) Moderate degree positive or negative ±0.25 to 0.75

(c) Low degree positive or negative 0 to ±0.25

Q.3 Explain the Mathematical Methods of finding out Correlation.

Ans.: Correlation coefficient can be determined by the following methods -

(i) Karl Pearson’s Coefficient of Correlation (r) : Karl Pearson‟s Coefficient of Correlation is widely used in practice. It is an assumption of Karl Pearson‟s coefficient of correlation that linear relations exist in both the series.

This method is considered as the best measure because it provides the knowledge of directions of changes in data i.e. positive or negative, and also shows the degree of correlation which should always lie between +1 and -1.

46

Computation of Karl Pearson’s Coefficient of Correlation :

Direct Method Short cut Method

Formula -

(1) r = Σ xy

√(Σx2 X Σy2)

(2) r = Σxy

N. σx. σy

Here x = X - X & Y = Y – Y

N No. of observations

Σx Standard deviation of X-series

σy Standard deviation of Y-series

Formula -

(1) r = Σdxdy – N(X - A) (Y - A)

N. σx. σy

(2) r = N . Σdxdy – (Σdx X Σdy)

√[{N.Σd2 x –(Σdx)2}[{N.Σd2y-(Σdy]2}]

Here dx = X - Ax & dy = Y - Ay

A Assumed mean

(ii) Spearman’s Rank Correlation: When it is not possible to measure the perfect quantities due to absence of numerical facts, ranking figures are used. These ranks are determined according to the size of the data. Using ranks rather than actual observations gives the coefficient of rank correlation.

This method was developed by the British Psychologist Charles Edward Spearman in 1904. This measure is especially useful to measure honesty, beauty, skill, wisdom etc.

Computation of Rank Correlation :

(a) First assign the ranks to the data of both the series. Rank can be assigned by taking either the highest value as I or the lowest value as 1. But whether we start with the lowest value or the highest value we must follow the same method in case of both the variables.

(b) Take the difference of two ranks (R1-R2) i.e. (D) (c) Square the rank difference i.e. (D2) (d) Apply the formula -

rR = 6∑ D2 N(N2 - 1) Where - N No. of pairs of observations.


D (R1 – R2) In case of Tied Ranks or Equal Ranks: If some values are equal in a

distribution than average rank is given to those items. The formula for calculation of correlation will be :

RP = 1 – 6 ∑d2 + 1 (m3 - m) +1 (m3 –m) - - - - - - - - - - -

12 12 N (N2 – 1) M No. of items where ranks are common. (iii) Concurrent Deviation Method: This method is simplest of all methods. It is

useful to know correlation of short-term changes in time-series. Sometimes it is not necessary to know the actual degree of correlation but it is important to know the direction of correlation i.e. positive or negative. For this purpose concurrent Deviation method is appropriate.

Computation of Correlation:

- Compare each item of both the series from its previous item. If the second item is bigger put a (+) sign; if it is smaller put a (-); and if it is equal, put a sign of (=).

- Multiply the signs of both the series.

- Total the positive signs = (C) No. of concurrent deviations.

- Apply the formula:

rc = ± ± (2C - N)

N

Where –

C No. of concurrent deviation

N No. of pairs – 1

Q. 4 What is Probable Error and Standard Error? What are the rules of testing the significance of coefficient of Correlation.

Ans. Probable Error is an expected error in Karl Pearson‟s coefficient of correlation, which facilitates the upper limit and lower limit of possible correlation. With the help of probable error it is possible to determine the reliability of the value of the coefficient in so far as it depends on the conditions of random sampling. Formula to calculate probable error :

48

P.E = 0.6745 X (1 - r2)

√N

Where –

r Coefficient of correlation.

N No. of items

Standard Error: Now a day‟s Standard Error is preferred to probable error. Degree of standard error is standard deviation of sampling distribution in any statistics of random sampling.

Other things remaining the same, it is essential that standard error should be small as far as possible. Smaller the standard error, more uniformity will be there in sampling distribution.

S.E. of r = (1 - r2)

√N

Rules for Testing the Significance of Coefficient of Correlation:

(i) If coefficient of correlation is more than 6 times of probable error (r > 6 P.E), it is significant.

(ii) If r is less than P.E. (r < P.E) it is not significant.

(iii) If r is less than 0.3 P.E (r < 0.3 P.E) it is insignificant.

□□□


Chapter 12

Linear Regression

Q.1 Define Regression. Why are there two Regression Lines? Under what conditions

can there be only one Regression Line?

Ans.: Regression literally means “return”or “go back”. In the 19th century, Francis Galton at first used regression in his paper “Regression towards Mediocrity in Hereditary Stature” for the study of hereditary characteristics.

Use of regression in modern times is not limited to hereditary characteristics only but it is widely used for the study of expected dependence of one variable on the other.

Therefore, the method by which best probable values of unknown data of a variable are calculated for the known values of the other variable is called regression.

Regression helps in forecasting, decision making and in studying two or more variables in economic field. It also shows the direction, quality and degree of correlation.

Regression Lines :

Regression line is that line which gives the best estimate of dependent variable for any given value of independent variable. If we take the case of two variables X and Y, we shall have two regression lines as the regression of X on Y and the regression of Y on X.

Regression Line X and Y : In this formation, Y is independent and X is dependent variable, and best expected value of X is calculated corresponding to the given value of Y.

Regression Line Y on X : Here Y is dependent and X is independent variable, best expected value of Y is estimated equivalent to the given value of X.

An important reason of having two regression lines is that they are drawn on least square assumption which stipulates that the sum of squares of the deviations from different points to that line is minimum. The deviations from the points from the line of best fit can be measured in two ways – vertical, i.e. parallel to Y – axis, and horizontal i.e. parallel to X axis.

50

For minimizing the total of the squares separately, it is essential to have two regression lines.

Single line of Regression : When there is perfect positive or perfect negative correlation between the two variables (r = ±1) the regression lines will coincide or overlap and will form a single regression line in that case.

Q.2 What is the difference between Regression and Correlation?

Ans.: Difference between Correlation & Regression :

Basis Correlation Regression

Relationship Correlation tells the degree of average relationship between two or more variables.

Using relationship between known variables and unknown variables, the unknown variable is estimated

Cause & Effect Unable to tell which series is the cause and which is the effect, despite high degree of correlation.

The given independent variable is the „cause‟ and dependent variable is the effect.

Change in scale Unaffected by the change of origin and scale.

Regression coefficient is affected by change in scale.

Application Limited Application. Wider Application.

Q.3 How are Regression Equations derived? Explain.

Ans.: Computation of Regression Equations : Algebraic expression of regression lines is called regression equations. Like lines equations are also two :

Regression Equation X on Y Regression Equation Y on X

Original Form :

X = a + by

Formula :

X - X = bxy (Y - Y)

Original Form :

Y = a + bx

Formula :

Y - Y = byx (X - X)


Here -

X Mean of x series.

Y Mean of y series.

bxy Regression coefficient X on Y

Here -

X Mean of x series.

Y Mean of y series.

byx Regression coefficient Y on X

Computation of Regression Coefficients :

1. Direct Method : bxy = Σxy Σy2

or bxy = r σx

σy

1. Direct Method : byx = Σxy Σx2

or byx = r σy

σx 2. Short Cut Method :

bxy = N. Σdxdy – (Σdx . Σdy)

N.Σd2y – (Σdy)2

Here - dx = X - A

dy =Y - A

2. Short Cut Method :

bxy = N. Σdxdy – (Σdx . Σdy)

N.Σd2x – (Σdx)2

Here - dx = X - A

dy =Y - A

Q.4 Give the interpretation of Regression Coefficients. How Correlation is calculated from Regression Coefficients?

Ans.: Interpretation of Regression Coefficients :

(i) If both the coefficients are positive correlation coefficient will be positive, and if both the coefficients are negative, the coefficient of correlation will also be negative.

(ii) Both the regression coefficients will have the same sign.

(iii) The product of both the regression coefficients cannot be more than 1.

Calculation of Correlation Coefficient from Regression Coefficient :

r = (bxy) X (byx)

bxy Regression coefficient x on y

byx Regression coefficient y on x.

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52

Chapter 13

Index Numbers

Q.1 What is Index Numbers? Give the importance or utility of Index Numbers?

Ans.: Index Numbers are specialized averages designed to measure the change in a group of related variables over a period of time. Index numbers have today become one of the most widely used statistical devices and there is hardly any field where they are not used.

According to Spiegel, “An Index Number is a statistical measure designed to show changes in a variable or a group of related variables with respect to time, geographic location or other characteristics such as income, profession etc.”

Importance of Index Numbers :

(i) Help in Framing Suitable Policies : Index numbers provide guidance in administrative policy determination. For example in determining dearness allowance of the employees cost of living index are used.

(ii) They Reveal Trends : Index numbers are most widely used for determining the commercial and industrial trends. By examining the index numbers of industrial production of last few years, we can conclude about the trend of production.

(iii) Helps in Comparative Study : Data which cannot be compared with the help of simple averages, index numbers can be used because they are in relative form.

(iv) Important in Forecasting : Index numbers are often used in time series analysis, the historical study of long-term trend, seasonal variations etc.

(v) Universal Application : Index numbers are useful in economic, commercial, social and in every field such as agriculture etc.


Q.2 What is Base Year. Distinguish between Fixed Base Method and Chain Base Method.

Ans.: Base year is such a year with which the changes in the current year are compared. Base year should be normal year from every aspect and it should not be affected by war, famines, inflation etc.

Base year should not be too old. The index for base period is always taken as 100.

In fixed base method, the year selected for construction of index numbers remains constant for all times and the base shall remain fixed.

While in chain base method the base year is changed every year, generally preceding year and not fixed year.

Q.3 Give the types of Weights. Why are Weights used in construction of Index Numbers?

Ans.: The term „Weight‟ refers to the relative importance of the different items in the construction of the index. For example in daily use the importance of wheat and rice is more than jute and iron.

Weights can be classified as follows -

(i) Explicit and Implicit weights : Explicit weights are called direct weight. They may be in the form of quantity or value. In implicit weighing, a commodity or its variety is included in the index a numbers of times.

(ii) Fixed and Fluctuating Weight : If same weights are used from year to year, they are called fixed weights. If weights are changed from time to time, they are called fluctuating weights.

(iii) Arbitrary and Real Weights : If real quantities or units are used, then those weights are called real weights.

If some unrealistic weights, according to the own will and assumptions of the investigator are used, they are called arbitrary weights.

Weights are used in construction of Index numbers because all items are not of equal importance and hence it is necessary to device some suitable method where by the varying importance of the different items is taken into account. This is done by allocating weights.

54

Q.4 Explain the various methods of constructing Index Numbers?

Ans.: Various methods of calculating index numbers can be shown by the following chart –

Index Numbers (P01)

Unweighted Weighted

Simple Aggregative

Simple Average of Relatives

Weighted Aggregative

Weighted Average of Relatives

Laspeyse’s Method

Paasche’s Method

Dorbish &

Bowley’s Method

Fishers Ideal

Method

Marshall Edgeworth

Method

Kelly’s Method

(I) Unweighted Index Numbers :

(a) Simple Aggregative Method :

P01 = ∑P1 X 100

∑P0

Where – ∑P1 Total of current year prices of various commodities. ∑P0 Total of base year prices of various commodities. (b) Simple Average of Relative Method :

P01 = ∑R and R = P1 X 100

N P0 Where – P1 Prices of current year. P0 Prices of base year.


Base year can be price of one year or multi-year or average price. Geometric mean can also be used for averaging the price relatives. (II) Weighted Index Numbers: (a) Weighted Aggregative Method:

(i) Lapser’s Method:

P01 = ∑P1 q0 X 100

∑P0 q0 Where – P1 Price of current year. P0 Price of base year. q0 Quantity of base year (ii) Paasche’s Method: P01 = ∑P1 q1 X 100 ∑P0 q1 Where – q1 Quantity of current year. (iii) Dorbish & Bowley’s Method:

P01 = Laspeyre‟s Index + Paasche‟s Index

2

or P01 = ∑P1 q0 + ∑P1 q1

∑P0 q0 ∑P0 q1 X 100

2

(iv) Marshall - Edge worth’s Method:

P01 = ∑P1 q0 + ∑P1 q1

∑P0 q0 + ∑P0 q1 X 100

2

(v) Fisher’s Ideal Method:

P01 = ∑P1 q0 X ∑P1 q1 X 100 or L X P

∑P0 q0 ∑P0 q1

(iv) Kelly’s Method:

P01 = ∑P1 q X 100

∑P0 q

56

Where – q = q0 + q1

2

(b) Weighted Average of Relatives: In this method, the price relatives for each commodity are obtained and these price relatives are multiplied by the value weights for each item and the product is divided by the total of weights.

Consumer price index = ΣRW

ΣW

Where R = P1 X 100 and W = P0 q0

P0

Q.5 Fisher’s Formula is called the Ideal Formula. Why?

Ans.: Fisher‟s formula is called the ideal because of the following reasons:

(i) It is based on geometric mean which is considered best for constructing index numbers.

(ii) It fulfills both the time reversal and factor reversal tests.

(iii) It takes into account both current year as well as base year prices and quantities.

(iv) It is free from bias.

Q.6 Explain the various tests of adequacy of Index Number.

Ans.: Following tests are applied for choosing an appropriate formula -

(i) Time Reversal Test : Time reversal test is a test to determine whether a given method will work both ways in time, forward and back ward. This test means that if the index number of the current year is computed on the basis of base year (P01) and again the index number of the base year is calculated on the basis of current year (P10), both the index numbers should be reciprocal of each other i.e. product of both of them should be one.

Symbolically, the following relation should be satisfied -

P01 X P10 = 1

(ii) Factor Reversal Test : According to this test, an index of price, if multiplied by an index of quantity, with the same base, given years and commodities, should be equal to the true value ratio, i.e. equal to the ratio of current year price to total price of the base year.


P01 XQ01 = ΣP1q1

ΣP0q0

If the product is not equal to the value ratio, there is, with reference to this test, an error in one or both of the index numbers.

(iii) Circular Test: This test is just an extension of the time reversal test. The test requires that if an index is constructed for the year „a‟ on base year „b‟ and for the year ‟b‟ on base year „c‟, we ought to get the same result as if we calculated directly an index for „a‟ on a base year „c‟ without going through „b‟ as an intermediary. So, if there are three indices P01, P12 and P20, the circular test will be satisfied if :

P01 X P12 X P20 = 1

Q.7 What are the methods of constructing Consumer Price Index or Cost of Living Index Numbers?

Ans.: Consumer price index or cost of living index numbers are designed to measure the effect of changes in the price of group of commodities and services on the purchasing power of a particular class of society, during any given period with reference to some fixed base. Its object is to find out how much the consumers of a particular class have to pay more for a certain basket of goods and services in a given period as compared to the base period.

Following two methods are used to construct consumer price index numbers -

(i) Family Budget method or weighted average of relatives method.

(ii) Aggregative Expenditure Method.

Family Budget Method : In this method, the price relatives for each commodity are obtained and these price relatives are multiplied by the value weights for each item and the product is divided by the total of weights.

Consumer price index = ΣRW

ΣW

Where R = P1 X 100 and W = P0 q0

P0

This method is same as weighted average of price relatives method.

58

Aggregative Expenditure Method : This method is most popular method for constructing consumer price index numbers. The prices of commodities of current year as well as base year are multiplied by the quantities consumed in the base year. The aggregate expenditure of current year is divided by the aggregate expenditure of the base year and the quotient is multiplied by 100.

Consumer price Index = ΣP1q0 X 100

ΣP0q0

This method is same as Laspeyre‟s method.

Q.8 What do you understand by base Shifting? Give the formula for converting the Fixed Base Index Number to Chain Base Index Number.

Ans.: Sometimes it becomes necessary to change the base year used for calculating index number of a series from one period to another without returning to the original date. This change of reference base period is usually referred to as „shifting the base‟.

Formula for converting Fixed Base Index to Chain Base Index -

Chain Base Index No. = Fixed base Index of Current Year X 100

Fixed base Index of Previous Year

Q.9 What is Splicing?

Ans.: When a series of index numbers is prepared by taking a particular year as base and then it is stopped, and the last year of that series is taken as the base year and another series is prepared. At times, it may be necessary to convert these two series into a continuous series. This procedure is called splicing.

If old series is to be related with new series, this is called forward splicing and to convert old series on the basis of new series is known as backward splicing.

a) Formula for Forward Splicing :

Old Index No. of new base year X Index No. to be adjusted

100

b) Formula for Backward Splicing :

Index No. to be adjusted X 100

Old Index No. of new base year

Q.10 What do you mean by Deflating of Index Numbers?

Ans.: Deflating means making allowances for the effect of changing price levels. A rise in price level means a reduction in the purchasing power of money.


The process of adjusting a series of salary or wages or income according to current price changes to find out the level of real salary, wages or income is called deflating of index numbers. It is necessary when price level is increasing and cost of living is also increasing.

Index No. of real wage = Real wage of current year X 100

Real wage of base year

Where Real wage = Money wage or income X 100

Price Index or Cost of living index

□ □ □

60

Practical Questions

Q.1 Calculate Mean, Mode and Median for the following data :

Wages in ` Below

13 13-15 15-17

Below

19

Below

21 21-23

Belo

w25

No. of Labourers 30 50 60 210 260 40 330

Solution.

Calculation of Mean, Mode and Median

Wages in

`

Frequency

M.V.

X-A

A = 18

Step

11-13

15-15

15-17

17-19

19-21

21-23

23-25

30

50

60

70 (210-140)

50 (260-210)

40

30(330-300)

12

14

16

18

20

22

24

-6

-4

-2

0

+2

+4

+6

-3

-2

-1

0

+1

+2

+3

-90

-100

-60

0

50

80

90

30

80

140

210

260

300

330

Total N=330 -30

Mean : = A x i = 18 + = 18 - 18-0.18 = ` 17.82

Mode (z) : By inspection method, the modal group is 17-19

Z = + x i where = 70 – 60 = 10, = 70 – 50 = 20

Thus, Z = 17 + x 2 or 17 + 0.67 =` 17.67

Median m = item = 165th

item. It lies in the median group = (17-19)

M = + (m-c) or 17+ (165-140) or 17 = or 17 = 0.71 = ` 17.71


Q.2 Complete mean and standard deviation of the marks obtained by 100 students in an

examination.

Computation of Mean and Std. Deviation

Marks No. of

Students

( )

Mid

Value (X)

dx

A = 25, i

=10

(4x5)

0-10

10-20

20-30

30-40

40-50

12

21

23

34

10

5

15

25

35

45

-2

-1

0

+1

+2

-24 -21 0

34 20

48 21 0

34 40

Total 100 (N) -

143

= A or marks

or

or

= 11.92 Marks

Thus Marks and

Q.3 The results of B.Com. Examination are given below: From the following data, calculate

coefficient of correlation between age and success in the examination.

Age in Years 18 19 20 21 22 23 24 25 26 27

% of failure 38 40 35 32 34 37 42 46 52 56

Sol. In the problem the percentage of failures is given, but coefficient of correlation is required to

ascertain in age and success in examination. As such [100- percentage of failure] will be the

% of success in the examination. Thus series shall be presented as under:

Age in

years (X)

% of success

100-% of

failure (Y)

18

19

20

21

22

23

-5 -4 -3 -2 -1 0

25 16 9 4 1 0

62

60

65

68

66

63

3 1 6 9 7 4

9 1

36 81 49 16

-15 -4

-18 -18 -7 0

Marks 0.10 10.20 20.30 30.40 40.50 Total

Frequency 12 21 23 34 10 100

62

24

25

26

27

1 2 3 4

1 4 9

16

58

54

48

44

-1 -5

-11 -15

1 25

121 225

-1 -10 -33 -60

(N=10)

=564

r =

Substituting the values formula, we get:

r =

=

= =0.774

=- A.L. [log of 1670 – ½ (log 825 + log 5636)]

=- A.L. [log 3.2227- 1/2 (2.9165 +3.7513)]

=- A.L. [3.2227-3.3339] = - A.L. or – 0.7741

It shows high degree of negative correlation.

Q.4 Calculate the regression equations from the following data:

1 2 3 4 5 6 7 8 9

Y 9 8 10 12 11 13 14 16 15

A =5

A =12

1

2

3

4

5

6

7

8

-4

-3

-2

-1

0

1

2

3

16

9

4

1

0

1

4

9

9

8

10

12

11

13

14

16

-3

-4

-2

0

-1

+1

+2

+4

9

16

4

0

1

1

4

16

12

12

4

0

0

1

4

12


Sol.

Thus N = 9, ΣX = 45,

ΣY = 108, Σ = 60,

Σ = 60, Σ = 57,

= or 5

Regression Coefficients (b) :

or

= 0.95

Regression Equation x on y

Or (X-5) = .95 (Y-12)

Or X = .95y – 11.4 + 5

Or X= 0.95y – 6.4

= or 12

Regression Coefficients (b)

or

= 0.95

Regression Equation y on x

Or (Y-12) = .95 (Y-5)

Or y = 0.95x - 4.74 + 12

Or y = .95y + 7.25

Q.5 An enquiry into the budgets of middle class families of Jodhpur gave the following

information:

Expenses on Price 2011 Price 2012 Standard Price

(`) Food Rent Clothing

35% 15% 20%

150 30 75

145 30 65

100 25 50

9 4 16 15 +3 9 12

45 0 60 108 0 60 57

64

Fuel Miscellaneous

10% 20%

25 40

25 45

20 40

What changes in the cost of living figures of 2011 and 2012 are seen as compared to

standard price? Also find out the percentage increase in prices in 2012 as compared to

2011? Sol. This question is of Family Budget Method. Hence, first price relative (R1 & R2) will be

computed on the basis of standard prices by using following formula:

= x 100, =

Construction of Cost of Living Index Nos.

Groups

Std.

Price

Price

2011

Price

2011

W

W W

Food Rent Clothing Fuel Miscellaneous

100

25

50

20

40

150

30

75

25

40

145

30

65

25

45

150 120 150 125 100

145 120 130 125

112.5

35

15

20

10

20

5250 1800 3000 1250 2000

5075 1800 2600 1250 2250

Total - - 100

( )

13,300 ( )

12975 ( )

Cost of Living Index for 2011 = or = 133.00

Cost of Living Index for 2012 = or = 129.75

Prices in 2012 have fallen (133-129.75) = 3.25 Percentage decline = x 2.44%

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